Method of increasing the flexibility of an AMOLDED display, a flexible display, and a product

ABSTRACT

A flexible AMOLED display is disclosed including an OLED stack having an anode layer, a cathode layer and an organic light emitting layer between the anode layer and the cathode layer. A backplane includes a substrate, a plurality of bus lines, and a thin film transistor array. A permeation barrier layer is positioned between the OLED stack and the backplane, and a plurality of vias connect the OLED anode layer to the backplane thin film transistor array. In one embodiment, a neutral plane of the AMOLED display crosses the permeation barrier. In one embodiment, the thickness of at least a portion of the bus lines is greater than the thickness of the cathode layer. A method of increasing the flexibility of an AMOLED display is disclosed. A method of assembling a flexible AMOLED display under a processing temperature of less than 200 degrees Celsius is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/918,265, filed Mar. 12, 2018 and issued Nov. 26, 2019, which is adivisional of U.S. patent application Ser. No. 15/177,520, filed Jun. 9,2016 and issued Apr. 17, 2018, which is a non-provisional of U.S. PatentApplication Ser. No. 62/180,881, filed Jun. 17, 2015, all of which areincorporated herein by reference in their entireties.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to flexible displays and devices such asorganic light emitting diodes and other devices, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

There is a desire to create displays with increased flexibility, andeven rollable displays. For an AMOLED display to be rollable, all of itskey components must be rollable. The components that are least amenableto being bent and flexed to very tight radius of curvature are thosethat are composed of stiff, inorganic materials. However, backplanecomponents are typically composed of stiffer materials. For example,within a typical AMOLED backplane, the transistors are often composed ofstiff materials. To improve flexibility, the transistors are constructedto be small in size and isolated from each other in “islands” as thisimproves flexibility of the transistor array within the backplane. Infurther consideration, it is known that tensile stress is generally moredamaging to device architecture than compressive stress, as it causesfilms to delaminate and crack, while compressive stress causes films tobuckle. OLEDs tend to be flexible, given they are a stack of organicmaterials sandwiched between two electrodes. However, this architecturestill does not achieve the level of flexibility desired, as the overalldevice layers are still subject to tensile stresses. The mainlimitations to flexibility will be low resistance metal bus linesrequired to pass data and scan signals from the display periphery to thebackplane circuits in the interior pixels, as well as to provide powerto the OLED devices themselves.

As bending radii for flexible and foldable displays become smaller andsmaller, the stresses and strains become larger. For rollable displays,there are many factors that must be taken into consideration to avoidfilms delaminating or cracking. OLEDs in particular have been shown towithstand bending to radius of curvature around 1 mm, and organic andoxide TFTs have shown themselves to also be very flexible when patternedinto small islands. Design approaches that advantageously utilize theneutral plane for minimizing strain have been previously proposed. Forexample, positioning thin film photonic devices at the neutral planeinside a multi-layer stack has been suggested for minimizing strainduring bending. See Juejun Hu et al., “Flexible integrated photonics:where materials, mechanics and optics meet [Invited],” Opt. Mater.Express 3, 1313-1331 (2013).

To further improve flexibility, backplane components are also beingconstructed of organic materials. To avoid outgassing from the backplanefrom “poisoning” the organic materials in the OLED, it is desirable toplace a permeation barrier in between the backplane and OLED in anAMOLED display. This permeation barrier could also serve as aplanarization layer, but would probably be a separate layer placed overa planarization layer, which typically would be an organic material. Asthis permeation barrier would be continuous, it would be verysusceptible to cracking and delamination under high tensile stress.

Thus, what is needed in the art is an improved flexible display thatreduces the strain in a permeation barrier placed in an AMOLED displayand improves the permeation barrier's ability to be repetitively flexed.

SUMMARY OF THE INVENTION

According to an embodiment, a flexible AMOLED display includes an OLEDstack having an anode layer, a cathode layer and an organic lightemitting layer between the anode layer and the cathode layer; abackplane having a substrate, a plurality of bus lines, and a thin filmtransistor array; a permeation barrier layer between the OLED stack andthe backplane; and multiple vias connecting the OLED anode layer to thebackplane thin film transistor array. In one embodiment, a neutral planeof the AMOLED display crosses the permeation barrier. In one embodiment,the neutral plane of the AMOLED display crosses the permeation barrierlayer multiple times. In one embodiment, the thickness of at least aportion of the bus lines is greater than the thickness of the cathodelayer. In one embodiment, the flexible display includes a planarizationlayer between the permeation barrier layer and the backplane. In oneembodiment, the flexible display includes a passivation layer betweenthe permeation barrier layer and the backplane. In one embodiment, thethin film transistor array includes an organic active layer. In oneembodiment, the thin film transistor array includes an organic gateinsulator. In one embodiment, the flexible display includes a thin filmbarrier disposed over the OLED stack. In one embodiment, when the AMOLEDdisplay is in a flexed state, a first portion of the permeation barrierlayer is in compressive stress and a second portion of the permeationbarrier layer is in tensile stress. In one embodiment, the OLED stackcathode layer is a continuous plane of conductive material. In oneembodiment, the OLED stack cathode layer has a substantially uniformthickness. In one embodiment, the OLED stack cathode layer includes atransparent material. In one embodiment, the permeation barrier layerincludes a transparent material. In one embodiment, the backplanesubstrate has a glass transition temperature of less than 200 degreesCelsius. In one embodiment, the permeation barrier layer has a glasstransition temperature of less than 200 degrees Celsius. In oneembodiment, the permeation barrier layer comprises a thin inorganicfilm. In one embodiment, the permeation barrier layer includes a mixtureof a polymeric material and a non-polymeric material as described inU.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 andPCT/US2009/042829, which are herein incorporated by reference in theirentireties. In one embodiment, a product including the flexible displayis selected from the group consisting of: a flat panel display, acomputer monitor, a medical monitor, a television, a touchscreen, aretractable projector screen, a billboard, a general illuminationdevice, a signal, a heads up display, a virtual reality display, anaugmented reality display, a fully transparent display, a large areawall, a theater, a stadium screen, and a sign.

In one embodiment, a flexible display includes an OLED having an anodelayer, a cathode layer and an organic light emitting layer between theanode layer and the cathode layer; a backplane circuit including aplurality of bus lines and a thin film transistor array; and apermeation barrier layer between the OLED stack and the backplanecircuit; where a plurality of vias through the permeation barrierconnect the OLED anode layer to the backplane circuit; and where thethickness of at least a portion of the bus lines is greater than thethickness of the cathode layer. In one embodiment, a neutral plane ofthe AMOLED display crosses the permeation barrier layer at least once.In one embodiment, the flexible display includes a planarization layerbetween the permeation barrier layer and the backplane circuit. In oneembodiment, the flexible display includes a passivation layer betweenthe permeation barrier layer and the backplane circuit. In oneembodiment, the thin film transistor array comprises an organic activelayer. In one embodiment, the thin film transistor array comprises anorganic gate insulator. In one embodiment, the flexible display includesa thin film barrier disposed over the OLED. In one embodiment, when thedisplay is in a flexed state, a first portion of the permeation barrierlayer is in compressive stress and a second portion of the permeationbarrier layer is in tensile stress. In one embodiment, the OLED cathodelayer is a continuous plane of conductive material. In one embodiment,the OLED cathode layer has a substantially uniform thickness. In oneembodiment, the OLED cathode layer includes a transparent material. Inone embodiment, the permeation barrier layer includes a transparentmaterial. In one embodiment, the backplane circuit includes a substratewith a glass transition temperature of less than 200 degrees Celsius. Inone embodiment, the permeation barrier layer has a glass transitiontemperature of less than 200 degrees Celsius. In one embodiment, thepermeation barrier layer includes a thin inorganic film. In oneembodiment, a product including the flexible display is selected fromthe group consisting of: a flat panel display, a computer monitor, amedical monitor, a television, a touchscreen, a retractable projectorscreen, a billboard, a general illumination device, a signal, a heads updisplay, a fully transparent display, a large area wall, a theater, astadium screen, and a sign.

In one embodiment, a method of increasing the flexibility of an AMOLEDdisplay having an OLED, a backplane circuit and a permeation barrierlayer between the OLED and backplane circuit, includes the steps ofmaintaining a substantially uniform thickness in a cathode layer of theOLED and varying the thickness of bus lines in the backplane circuit,such that a neutral plane of the AMOLED display crosses the permeationbarrier player at least once.

In one embodiment, a method of assembling a flexible AMOLED displayincludes the steps of forming a backplane circuit including a pluralityof bus lines and a thin film transistor array onto a flexible substrate;depositing a permeation barrier layer over the backplane circuit;etching a plurality of vias into the permeation barrier layer; anddisposing an OLED having an anode layer, an OLED stack and an OLEDcathode layer over the permeation barrier layer; where the processingtemperature when assembling the flexible AMOLED display is less than 200degrees Celsius. In one embodiment, the method includes the step ofplanarizing the backplane. In one embodiment, the method includes thestep of passivating the backplane. In one embodiment, the methodincludes the step of disposing a thin film barrier over the OLED. In oneembodiment, the method includes the step of disposing a plastic filmover the flexible AMOLED display. In one embodiment, the method includesthe step of positioning at least a portion of the permeation barrierlayer on both sides of a neutral plane of the assembled AMOLED display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a schematic of a flexible display according to oneembodiment.

FIG. 4 is a flow chart of a method for assembling a flexible display.

DETAILED DESCRIPTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a more clear comprehension of the present invention, whileeliminating, for the purpose of clarity, many other elements found inflexible displays. Those of ordinary skill in the art may recognize thatother elements and/or steps are desirable and/or required inimplementing the present invention. However, because such elements andsteps are well known in the art, and because they do not facilitate abetter understanding of the present invention, a discussion of suchelements and steps is not provided herein. The disclosure herein isdirected to all such variations and modifications to such elements andmethods known to those skilled in the art.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are described.

As used herein, each of the following terms has the meaning associatedwith it in this section.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e., to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

“About” as used herein when referring to a measurable value such as anamount, a temporal duration, and the like, is meant to encompassvariations of ±20%, ±10%, ±5%, ±1%, and ±0.1% from the specified value,as such variations are appropriate.

Ranges: throughout this disclosure, various aspects of the invention canbe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Where appropriate, the description of a range should beconsidered to have specifically disclosed all the possible subranges aswell as individual numerical values within that range. For example,description of a range such as from 1 to 6 should be considered to havespecifically disclosed subranges such as from 1 to 3, from 1 to 4, from1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well asindividual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5,5.3, and 6. This applies regardless of the breadth of the range.

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques, sputtering or vacuumthermal evaporation, and may include compositions having a single phaseas well as compositions having multiple phases. Any suitable material orcombination of materials may be used for the barrier layer. The barrierlayer may incorporate an inorganic or an organic compound or both. Thepreferred barrier layer comprises a mixture of a polymeric material anda non-polymeric material as described in U.S. Pat. No. 7,968,146, PCTPat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which areherein incorporated by reference in their entireties. To be considered a“mixture”, the aforesaid polymeric and non-polymeric materialscomprising the barrier layer should be deposited under the same reactionconditions and/or at the same time. The weight ratio of polymeric tonon-polymeric material may be in the range of 95:5 to 5:95. Thepolymeric material and the non-polymeric material may be created fromthe same precursor material. In one example, the mixture of a polymericmaterial and a non-polymeric material consists essentially of polymericsilicon and inorganic silicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. Such consumer products would include anykind of products that include one or more light source(s) and/or one ormore of some type of visual displays. Some examples of such consumerproducts include flat panel displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, virtual reality displays,augmented reality displays, laser printers, telephones, cell phones,tablets, phablets, personal digital assistants (PDAs), laptop computers,digital cameras, camcorders, viewfinders, micro-displays, 3-D displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Active matrix backplanes may consist of circuitscontaining thin film transistors, whose active layer may be either anorganic or inorganic semiconductor. Many of the devices are intended foruse in a temperature range comfortable to humans, such as 18 degrees C.to 30 degrees C., and more preferably at room temperature (20-25 degreesC.), but could be used outside this temperature range, for example, from−40 degree C. to +80 degree C.

With reference now to FIG. 3, a flexible and rollable AMOLED display 300according to one embodiment includes a backplane 320 having multiple buslines 324 that carry power to the OLED 340 in the front plane. The OLED340 includes an anode 342, a cathode 346 and an organic light emittinglayer 344 therebetween. It should be appreciated that the frontplaneOLED architecture may include any number of organic layers or stacks, asdesired. In this example, the OLED power lines/bus lines 324 require thelowest resistance, and therefore are the thickest conductors. The OLEDpower is carried by the bus line 324 in the backplane 320 that connectsto the drain/source of a thin film transistor (TFT) 326. The othersource/drain terminal of the TFT 326 will contact the OLED anode 342 byway of a via 328 connecting the TFT backplane 320 to the OLED stack 340.The OLED power will also flow from its cathode 346, and in general, thisis an unpatterned low resistance layer, which can be solid metal for abottom emission device, or transparent for a top emission device. A topprotective or sealing layer 348 such as a thin plastic film may also beincluded. Since the backplane TFT may be composed of organic materials,either because of its active materials (e.g. organic TFTs using organicactive layer or gate insulator), or because of the use of organicplanarization or passivation layers used to prepare the TFT for OLEDdeposition, a permeation barrier 330 may be incorporated into thedisplay 300 to prevent organic films from the backplane 320 outgassingand reducing the lifetime of the OLED 340.

When a thin display is flexed, there is a theoretical neutral plane thatruns through the display which defines a plane which does not expand orcontract on flexing. Regions on one side of the neutral plane will be intensile stress and regions on the other side will be in compressivestress. The closer a material is to the neutral plane, the less stressis imposed on the material during flexion. Thus, to minimizedelamination or cracking of materials, it is desirable to design a thindisplay such that stiff or inorganic materials are as close to theneutral plane as possible.

The calculation of the neutral plane is related to the thickness,position and Young's modulus of the individual layers or films making upthe display. The neutral plane will be in the middle of a symmetricalstructure, and can be moved away from this position by materials havinga large Young's modulus multiplied by their thickness, particularly ifthese films are placed away from the middle of the device. Within theOLED stack it will be the current carrying electrodes for the OLED thatwill have the largest Young's modulus, and so the position and thicknessof these electrodes will in part determine where the neutral planetheoretically resides within the device.

With reference now specifically to FIG. 3, the cathode 346 is generallya continuous plane of conductive material, and this will tend to movethe display neutral plane 350 towards the upper display surface, andaway from the permeation barrier 330. Bus lines 324 in the backplane 320near the TFT 326 will tend to pull the neutral plane 350 down towardsthe substrate 322. If the bus lines 324 in the backplane 320 are thickerthan the cathode thickness d_(cathode), and a similar distance away fromthe center of the display 300, then the bus lines 324 will pull theneutral plane 350 below the center of the display 300, overcoming theeffect of the OLED cathode 346. By suitably selecting the relativethickness of the cathode d_(cathode) and bus lines d_(busline), theneutral plane 350 can cross the center of the display 300, depending onthe position of the bus lines 324 in the TFT backplane 320. This ensuresthat when display 300 is flexed, the stress in the continuous permeationbarrier 330 placed in the display 300 will include minimal amounts ofboth compressive and tensile stress, dependent on the pitch of the buslines 324. Accordingly, by uniquely controlling the cathode and bus linethickness, the amount and occurrence of cracking caused by tensilestress can be reduced or eliminated. While the bus lines 324 arerequired to reduce voltage losses in the display, they can have asynergistic benefit to reduce any damage to an internal permeationbarrier 330 under tight flexing conditions.

Accordingly, in one embodiment, a method of increasing the flexibilityof an AMOLED display having an OLED, a backplane circuit and apermeation barrier layer between the OLED and backplane circuit,includes the steps of maintaining a substantially uniform thickness in acathode layer of the OLED and varying the thickness of bus lines in thebackplane circuit, such that a neutral plane of the AMOLED displaycrosses the permeation barrier player at least once.

With specific reference now to FIG. 4, a method of assembling a flexibleAMOLED display includes the steps of forming a backplane circuitincluding multiple bus lines and a thin film transistor array onto aflexible substrate 402, depositing a permeation barrier layer over thebackplane circuit 404, etching a plurality of vias into the permeationbarrier layer 406, and disposing an OLED having an anode layer, an OLEDstack and an OLED cathode layer over the permeation barrier layer 408.The processing temperature when assembling the flexible AMOLED displayis less than 200 degrees Celsius 410. A flexible substrate (e.g low costplastic such as, PET or PEN or else thin metal) is prepared, which caninclude an optional planarization layer), and optionally coated with atransparent and flexible permeation barrier. Bus lines are patterned onthe substrate, followed by TFT deposition and fabrication usingpatterning techniques such as photolithography. The TFT can beplanarized and passivated to provide good TFT stability and a smoothsurface onto which to deposit the OLED stacks. A permeation barrier(thin inorganic film or composite barrier) would be deposited over theplanarization layer, and a via etched into the device to allow for theOLED anode electrode to be deposited and connected to the backplanecircuit below. The OLED stack is then deposited, followed by a cathode.A thin film barrier will then be placed over the OLED to preventmoisture and oxygen from degrading the OLED. For additional mechanicalprotection a plastic film and optional hardcoat is often laminated overthe structure. The OLED could be bottom or top emission. It is alsopossible to omit the barrier layer on the bottom substrate if theinternal barrier layer is sufficiently effective at preventing oxygen ormoisture from degrading the OLEDs. In one embodiment, the methodincludes positioning at least a portion of the permeation barrier layeron both sides of a neutral plane of the assembled AMOLED display.Advantageously, low temperature processing allows the display to bemanufactured using a variety of highly flexible substrate materials(e.g. plastics) and processes that have a lower processing temperaturelimit.

The disclosures of each and every patent, patent application, andpublication cited herein are hereby incorporated herein by reference intheir entirety. While this invention has been disclosed with referenceto specific embodiments, it is apparent that other embodiments andvariations of this invention may be devised by others skilled in the artwithout departing from the true spirit and scope of the invention.

We claim:
 1. A method of increasing the flexibility of an AMOLED displayhaving an OLED, a backplane circuit and a permeation barrier layerbetween the OLED and backplane circuit, comprising maintaining asubstantially uniform thickness in a cathode layer of the OLED andvarying the thickness of bus lines in the backplane circuit, such that aneutral plane of the AMOLED display crosses the permeation barrier layerat least once.
 2. The method of claim 1, further comprising the step ofplanarizing the backplane.
 3. The method of claim 1, further comprisingthe step of passivating the backplane.
 4. The method of claim 1, furthercomprising the step of disposing a thin film barrier over the OLED. 5.The method of claim 1, further comprising the step of disposing aplastic film over the OLED.
 6. The method of claim 1, wherein theneutral plane of the AMOLED display crosses the permeation barriermultiple times.
 7. The method of claim 1, wherein the thickness of atleast a portion of the bus lines is greater than the thickness of thecathode layer.
 8. The method of claim 7, wherein the thickness of thebus lines is greater than the thickness of the cathode layer.
 9. Aflexible display produced by the method of claim
 1. 10. A productcomprising the flexible display of claim 9, wherein the product isselected from the group consisting of: a flat panel display, a computermonitor, a medical monitor, a television, a touchscreen, a retractableprojector screen, a billboard, a general illumination device, a signal,a heads up display, a fully transparent display, a virtual realitydisplay, an augmented reality display, a large area wall, a theater, astadium screen, and a sign.